PTC heater with flexible printed circuit board

ABSTRACT

An electrically heated chemical delivery system including a heat sensitive chemical and an electrical heater adjacent to the heat sensitive chemical. The heater includes a heater element with a first heater side and a second heater side and a flexible printed circuit in electrical contact with both the first heater side and the second heater side. The flexible printed circuit includes at least one fold allowing electrical contact with both the first heater side and the second heater side.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a non-provisional application based upon U.S. provisional patentapplication Ser. No. 60/357,517, entitled “PTC HEATER WITH FLEXIBLEPRINTED CIRCUIT BOARD”, filed Feb. 15, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrically heated chemicaldelivery system, and, more particularly, to a PTC electrical heaterincluding a flexible printed circuit.

2. Description of the Related Art

A positive temperature coefficient of resistance (PTC) material exhibitsthe characteristic that, as the temperature of the material rises, theelectrical resistance of the material also rises. If an electricalcomponent is composed of PTC material, and if a voltage is applied tothe component, the component will dissipate energy at a rate of V²/Rwhere V is the applied voltage and R is the instantaneous resistance ofthe component. Unless sufficiently cooled, the PTC electrical componentwill heat up as a result of the dissipated energy and thereby increasethe material resistance which will decrease the electrical currentthrough the component and decrease the energy dissipation of thecomponent. The PTC component is therefore somewhat self limiting from anelectrical current point of view.

A Positive Temperature Coefficient (PTC) heater circuit applies anelectrical potential on opposite sides of a PTC material to generateheat. As the temperature of the PTC material increases, the electricalresistance also increases. Typical PTC heater circuits use an insulatingfilm and two metal electrodes in proximity to a heatsinking/distributive surface. Although this construction technique iseffective to produce a properly operating PTC heater, it can berelatively expensive in terms of fabrication and assembly.

What is needed in the art is a PTC heater which is easily and costeffectively fabricated.

SUMMARY OF THE INVENTION

The present invention provides a PTC heater including a flexible printedcircuit with printed electrodes on an insulative substrate.

The invention comprises, in one form thereof, an electrically heatedchemical delivery system, comprising a heat sensitive chemical and anelectrical heater adjacent to the heat sensitive chemical. The heaterincludes a heater element with a first heater side and a second heaterside and a flexible printed circuit in electrical contact with both thefirst heater side and the second heater side. The flexible printedcircuit includes at least one fold allowing electrical contact with boththe first heater side and the second heater side.

An advantage of the present invention is a PTC heater which is easilyand cost effectively fabricated.

Another advantage of the present invention is PTC material can beprinted on the flexible printed circuit.

Yet another advantage of the present invention is the flexible printedcircuit can include additional components, such as a fuse and indicatorlight with relatively small incremental manufacturing expense.

A yet further advantage of the present invention is a reduction in thenumber of parts required to assemble the electrical heater.

An even yet further advantage of the present invention is an increase inreliability due to the number of parts reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of an embodiment of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a side view of an embodiment of the electrically heatedchemical delivery system of the present invention showing a flexibleprinted circuit folded around a heater element; and

FIG. 2 is a plan view of the printed flexible circuit of FIG. 1 in anunfolded state.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplification set out hereinillustrates one preferred embodiment of the invention, in one form, andsuch exemplification is not to be construed as limiting the scope of theinvention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, there isshown an electrically heated chemical delivery system 10 which generallyincludes heat sensitive chemical 12 adjacent electrical heater 14. Heatsensitive chemical 12 is shown schematically in FIG. 1.

Heat sensitive chemical 12 can include, but is not limited to,fragrances, insecticides, air fresheners, aromatherapy chemicals,anti-mold compounds, anti-mildew compounds and other chemicals. Heatsensitive chemical 12 can be in the form of capsules, packets, gels,liquids, solids and the like. Heat sensitive chemical 12 and adjacentelectrical heater 14 are typically contained in a suitable housing (notshown). Upon receiving heat energy from heater 14, heat sensitivechemical 12 releases a portion of its chemical to the ambient.

Electrical heater 14 includes flexible circuit 16 (FIG. 2), which can bea flexible printed circuit, folded at least partially around heaterelement 18, and in electrical contact with both first heater side 36 andsecond heater side 38 of heater element 18. Heater element 18 caninclude positive temperature coefficient material 20 which can be anyone of many suitable PTC materials, or combinations thereof.Alternatively, flexible circuit 16 can be in electrical contact at leastone side of heater element 18.

Flexible circuit 16 includes a flexible insulating substrate 22,electrical traces 24 and indicator light 26. Insulating substrate 22 isformed of any suitable material which is flexible and has preselectedelectrical characteristics necessary for operation of electrical heater14. First circuit side 17 of flexible circuit 16 is shown as includingall of electrical traces 24 and indicator light 26, however, flexiblecircuit 16 can alternatively be a double sided printed circuit or amultilayer printed circuit.

Electrical traces 18 include leads 28, contact pads 30, 31 and printedfuse 32. Leads 28 are connected to a suitable source of electrical power(not shown). Contact pads 30, 31 electrically contact opposing sides ofheater element 18 when flexible circuit 16 is folded around heaterelement 18 (as shown in FIG. 1). Leads 28 are also connected in parallelwith each of contact pads 30, 31 and indicator light 26. Printed fuse 32is sized and configured to open at a preselected current therethrough.

Flexible circuit 16 carries electrical traces 24 thereon and is sizedand configured to fold around heater element 18, such as at fold lines34, shown as dashed lines in FIG. 2, and resulting, for example, infolds 40. The number of folds 40 is at least one but can include two ormore as dictated by the application. Likewise, the angle of folds 40,can be 90° as shown or can be other angles depending, in part, on thenumber of folds among other factors such as the flexibility of substrate22 and electrical traces 24. The particular location at which flexiblecircuit 16 is folded may vary from one application to another. Thespecific size, configuration and geometrical shape of flexible circuit16, electrical traces 24 and heater element 18 can be varied dependingon the application.

The method of assembling electrical heater 14 includes the steps ofelectrically connecting a first lead 28 of flexible printed circuit 16to first heater side 36 by electrically contacting first heater side 36with first contact pad 30; folding flexible printed circuit 16 at leastpartially around heater element 18; and electrically connecting secondlead 28 of flexible printed circuit 16 to second heater side 38 byelectrically contacting second heater side 38 with second contact pad31. Heater sides 36, 38 can be electrically connected to respectivecontact pad 30,31 with solder, conductive adhesives and the like.Electrical heater 14 is assembled with only two separate componentsthereby achieving the aforementioned manufacturing and reliabilityadvantages. Alternatively, positive temperature coefficient material 20can be printed on flexible circuit 16 at either of contact pads 30, 31.

In use, heat sensitive chemical 12 is located adjacent electrical heater14, typically by way of a suitable housing (not shown) or the like.Electrical heater 14 is connected to a suitable source of electricalpower (not shown) and thereby commences generating heat. Heat fromelectrical heater 14 reaches nearby heat sensitive chemical 12 therebydispersing some of the chemical of heat sensitive chemical 12 into theambient. Indicator light 26 can indicate when power is applied toelectrical heater 14.

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

1. An electrically heated chemical delivery system, comprising: a heatsensitive chemical; and an electrical heater adjacent said heatsensitive chemical, said heater including: a heater element having afirst heater side and a second heater side; and a flexible printedcircuit in electrical contact with both said first heater side and saidsecond heater side, said flexible printed circuit including at least onefold allowing said electrical contact with both said first heater sideand said second heater side, said flexible printed circuit including aflexible insulating substrate, a first lead electrically connected tosaid first heater side, a second lead electrically connected to saidsecond heater side, both of said first lead and said second lead printedon said flexible insulating substrate.
 2. An electrical heater,comprising: a heater element having a first heater side and a secondheater side; and a flexible printed circuit in electrical contact withboth said first heater side and said second heater side, said flexibleprinted circuit including at least one fold allowing said electricalcontact with both said first heater side and said second heater side,said flexible printed circuit including a flexible insulating substrate,a first lead electrically connected to said first heater side, a secondlead electrically connected to said second heater side, both of saidfirst lead and said second lead printed on said flexible insulatingsubstrate.